1. Field of the invention
The invention relates to an arrangement for sealing the slots in the laminated stator core of an electrical machine. The invention is based on a slot sealing arrangement according to the preamble of patent claim 1.
Slot sealing arrangements of said type are known, for example, from Brown Boveri Mitteilungen [Brown Boveri Memoranda], Year 54, September 1967, Number 9, pages 524-526.
2. Discussion of background
In the case of large electrical machines, in particular generators, winding bars are inserted in a known manner in slots in a laminated stator core, these slots being open toward an air gap. These slots are then sealed with respect to the air gap by means of slot sealing arrangements in order to secure the winding bars. In order to achieve maximum utilization of the radially acting excitation field from a generator rotor, the magnetic flux in the limiting case must penetrate exclusively radially into the teeth of the laminated stator core formed by the winding slots. However, since the slots have a width appropriate for the insertion of the winding bars, the radial penetration of the magnetic flux directly into the bars results in a certain element of the magnetic flux being lost. This loss element can be reduced in a noticeable manner by, as shown on pages 524-526 of Brown Boveri Mitteilungen [Brown Boveri Memoranda], Year 54, September 1967, Number 9, the winding slots in the laminated stator core being formed to be considerably deeper than is necessary for the embedding of the winding bars. Such arrangements thus have a winding slot with a so-called preliminary slot, facing the air gap of the electrical machine. The aim of this arrangement is that the more deeply located winding bars will lead to the radial magnetic flux being concentrated into the teeth of the laminated stator core, and thus to the radial field losses being markedly reduced.
An identical arrangement of stator winding bars in winding slots with preliminary slots in a laminated core is likewise shown in FIG. 4 in U.S. Pat. No. 4,028,569.
One common feature of the winding slots with preliminary slots known from the cited prior art is that they require a slot sealing arrangement of duplicated design. A first slot sealing arrangement is used to seal the winding slot in order to secure the winding bars in the slot, and a second slot sealing arrangement seals the preliminary slot from the machine air gap. The channel-like space which is formed between the first and second slot sealing arrangement is used for deliberate cooling of the teeth (which are thermally highly stressed in limit-rating machines) of the laminated stator core by means of a gaseous coolant.
Major disadvantages of the double slot sealing arrangement are considered to be that they have to be designed with a high level of production-engineering complexity, in which case the more deeply located slot sealing arrangement for the winding bars can be inspected only after removing the slot sealing arrangements in the preliminary slot, and, in addition, the fact that the cooling of the teeth of the laminated stator core is limited.